video: da8xx-fb: Fix casting of info->pseudo_palette

The casting to (u16 *) on info->pseudo_palette is wrong and causes the
display to show a blue (garbage) vertical line on every other pixel column

Signed-off-by: Jon Ringle <jringle@gridpoint.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>